Steam drying of products containing solvent mixtures

Drying experiments with single, porous spheres wetted with mixtures of 2-propanol and water were performed using superheated steam, air, or steam-air mixtures as drying agent. Both the drying rate and the moisture composition were determined experimentally for different temperatures and compositions of the drying agent and for different initial compositions of the moisture. It is shown that evaporation of 2-propanol is enhanced by using superheated steam as drying agent instead of air due to steam condensing on the sample. While the overall drying rate increases with rising steam temperature, the evaporation rate of 2-propanol is hardly affected. When drying samples containing mixtures of 2-propanol and water, internal boiling can occur depending on the vapor-liquid equilibrium. Vapor generated inside the sample may cause mechanical dewatering of the sample which greatly increases the drying rate.